1. Field of the Invention
The present invention relates to a knee airbag accommodated below an instrument panel.
2. Related Technology
A knee airbag is an occupant restraining device that is inflated and deployed in the vicinity of the occupant's knees when a vehicular accident occurs. By providing the knee airbag, it is possible to protect the occupant's knees from collision with the instrument panel and the like.
The knee airbag is mainly accommodated below the instrument panel, for example, inside the lower section of the steering column cover on the driver's seat side of the vehicle. To enable the attachment in a limited accommodation state, the knee airbag is compacted by folding or winding and attached in this state. When an accident occurs, the knee airbag receives the supply of gas from an inflator (gas generator) and is inflated and deployed inward of the occupant cabin of the vehicle.
The knee airbag should be inflated and deployed within a space from below the instrument panel to the occupant's knees. Since this space is extremely narrow, the knees cannot be prevented from colliding with the instrument panel, unless the inflation and deployment proceed rapidly. Therefore, the knee airbag is configured by using such measures as a folding method ensuring instantaneous deployment or a method enabling smoother inflow of the gas.
For example, Japanese Patent Application Publication No. 2004-330959 discloses an occupant airbag device of a bag-body type for protection of knees that is provided with an internal inflator inserted into a substantially cylindrical diffuser (flow adjusting device). According to this document, the first to third flow-adjusting openings of different opening areas are formed in the diffuser, and by using those openings, it is possible to deploy the knee-protecting airbag before the deployment of the bag for head and chest protection.
With the technique such as described in the above mentioned reference, the tubular diffuser has a large length, thereby making it possible to guide the gas at an accordingly high speed in the desired direction. Therefore, the airbag easily expands in the left-right direction, which is the longitudinal direction of the diffuser, and the deployment proceeds rapidly. However, outlet ports at both ends of such a long diffuser are closed by folding when the airbag is accommodated, thereby causing the so-called choking, that is, a state in which the gas cannot be smoothly ejected from both ends of the tubular diffuser when the airbag is inflated and deployed.